1. Technical Field
The present invention relates generally to pneumatic ratcheting mechanisms and in particular to a device to aid in shank spindle retainment during ratchet resetting.
2. Related Art
Pneumatic ratchets operate by reciprocating movement of a yoke that engages a pawl. The pawl is connected to a shank spindle and is selectively positionable such that the yoke, when it reciprocates, engages the pawl to forcibly turn the pawl and shank spindle in a selected direction. The shank spindle being in turn attached to a workpiece being operated upon.
In the related art, proper operation of the pneumatic ratchets is reliant on temporary frictional retainment of the shank spindle during the non-pawl-engaging resetting stroke of the yoke. For example, in U.S. Pat. No. 4,791,836 to D'Haem et al. (see FIG. 8), incorporated by reference herein, either a single ball bearing or a pair of ball bearings 21, mounted within the shank spindle 24, are spring biased into engagement with a rotationally fixed thrust washer(s) 23 of the ratchet to temporarily retain the shank spindle 24 from rotation while the yoke 17 moves through its reset stroke. This construction, however, has a number of drawbacks. For instance, use of the washers and bearings oftentimes does not adequately prevent rotation of the shank spindle because the bearings tend to have a relatively smooth surface and very low contact area. Furthermore, since the ball bearings may rotate relative to the spring and washers, the springs must be of such force as to maintain the bearings in high compression to prevent rotation. However, because the ball bearings take up space, the strength of the spring is limited to that which will fit between the ball bearings.
It is therefore a feature of the present invention to overcome the above shortcomings.